Patterning electrode materials free from berm structures for thin film photovoltaic cells

ABSTRACT

A method for forming a thin film photovoltaic device having patterned electrode films includes providing a soda lime glass substrate with an overlying lower electrode layer comprising a molybdenum material. The method further includes subjecting the lower electrode layer with one or more pulses of electromagnetic radiation from a laser source to ablate one or more patterns associated with one or more berm structures from the lower electrode layer. Furthermore, the method includes processing the lower electrode layer comprising the one or more patterns using a mechanical brush device to remove the one or more berm structures followed by treating the lower electrode layer comprising the one or more patterns free from the one or more berm structures. The method further includes forming a layer of photovoltaic material overlying the lower electrode layer and forming a first zinc oxide layer overlying the layer of photovoltaic material.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of and claims priority to U.S. patentapplication Ser. No. 12/565,735 filed on Sep. 23, 2009, which claimspriority to U.S. Provisional Patent Application No. 61/101,650, filed onSep. 30, 2008, the disclosures of which are incorporated by referenceherein in their entirety for all purposes.

BACKGROUND

The present invention relates generally to photovoltaic materials andmanufacturing method. More particularly, the present invention providesa method and structure for fabricating thin film solar cells. Merely byway of example, the present method includes patterning electrodematerial free from berm structures for manufacture of thin filmphotovoltaic cells, but it would be recognized that the invention mayhave other configurations.

From the beginning of time, mankind has been challenged to find way ofharnessing energy. Energy comes in the forms such as petrochemical,hydroelectric, nuclear, wind, biomass, solar, and more primitive formssuch as wood and coal. Over the past century, modern civilization hasrelied upon petrochemical energy as an important energy source.Petrochemical energy includes gas and oil. Gas includes lighter formssuch as butane and propane, commonly used to heat homes and serve asfuel for cooking Gas also includes gasoline, diesel, and jet fuel,commonly used for transportation purposes. Heavier forms ofpetrochemicals can also be used to heat homes in some places.Unfortunately, the supply of petrochemical fuel is limited andessentially fixed based upon the amount available on the planet Earth.Additionally, as more people use petroleum products in growing amounts,it is rapidly becoming a scarce resource, which will eventually becomedepleted over time.

More recently, environmentally clean and renewable sources of energyhave been desired. An example of a clean source of energy ishydroelectric power. Hydroelectric power is derived from electricgenerators driven by the flow of water produced by dams such as theHoover Dam in Nevada. The electric power generated is used to power alarge portion of the city of Los Angeles in California. Clean andrenewable sources of energy also include wind, waves, biomass, and thelike. That is, windmills convert wind energy into more useful forms ofenergy such as electricity. Still other types of clean energy includesolar energy. Specific details of solar energy can be found throughoutthe present background and more particularly below.

Solar energy technology generally converts electromagnetic radiationfrom the sun to other useful forms of energy. These other forms ofenergy include thermal energy and electrical power. For electrical powerapplications, solar cells are often used. Although solar energy isenvironmentally clean and has been successful to a point, manylimitations remain to be resolved before it becomes widely usedthroughout the world. As an example, one type of solar cell usescrystalline materials, which are derived from semiconductor materialingots. These crystalline materials can be used to fabricateoptoelectronic devices that include photovoltaic and photodiode devicesthat convert electromagnetic radiation into electrical power. However,crystalline materials are often costly and difficult to make on a largescale. Additionally, devices made from such crystalline materials oftenhave low energy conversion efficiencies. Other types of solar cells use“thin film” technology to form a thin film of photosensitive material tobe used to convert electromagnetic radiation into electrical power.Similar limitations exist with the use of thin film technology in makingsolar cells. That is, efficiencies are often poor. Additionally, filmreliability is often poor and cannot be used for extensive periods oftime in conventional environmental applications. Often, thin films aredifficult to mechanically integrate with each other. Furthermore, thinfilms are often difficult to manufacture in a cost effective, efficient,and reliable way. These and other limitations of these conventionaltechnologies can be found throughout the present specification and moreparticularly below.

SUMMARY

The present invention relates generally to photovoltaic materials andmanufacturing method. More particularly, the present invention providesa method and structure for fabricating thin film solar cells. Merely byway of example, the present method includes patterning electrodematerial free from berm structures for manufacture of thin filmphotovoltaic cells, but it would be recognized that the invention mayhave other configurations.

In a specific embodiment, the present invention provides a method forforming a thin film photovoltaic device having patterned electrodefilms. The method includes providing a soda lime glass substratecomprising a surface region and forming a lower electrode layercomprising a molybdenum material overlying the surface region. Themethod further includes subjecting the lower electrode layer with one ormore pulses of electromagnetic radiation from a laser source. The one ormore pulses of electromagnetic radiation is capable of ablating one ormore patterns from the lower electrode layer. The one or more patternsincludes one or more berm structures. Additionally, the method includesprocessing the lower electrode layer comprising the one or more patternsusing a mechanical brush device to remove the one or more bermstructures. The method further includes treating the lower electrodelayer comprising the one or more patterns free from the one or more bermstructures. Furthermore, the method includes forming a layer ofphotovoltaic material overlying the lower electrode layer. The layer ofphotovoltaic material comprising an interconnect structure based on theone or more patterns within the lower electrode layer. Moreover, themethod includes forming a first zinc oxide layer overlying the layer ofphotovoltaic material.

In another specific embodiment, the present invention provides a methodfor forming a thin film photovoltaic device having patterned electrodefilms. The method includes providing a soda lime glass substratecomprising a surface region and forming a lower electrode layercomprising a molybdenum material overlying the surface region. Themethod also includes subjecting the lower electrode layer with one ormore pulses of electromagnetic radiation from a laser source forablating one or more patterns from the lower electrode layer. The one ormore patterns includes one or more berm structures. Additionally, themethod includes processing the lower electrode layer comprising the oneor more patterns using a mechanical brush device and a cleaning liquidto remove the one or more berm structures. Furthermore, the methodincludes processing the lower electrode layer comprising the one or morepatterns free from the one or more berm structures using a gas knife.The gas knife is configured to remove substantially any liquid includingliquid droplets from a surface of the lower electrode layer to dry thelower electrode layer comprising the one or more patterns free from theone or more berm structures.

Many benefits are achieved by ways of present invention. For example,the present invention uses starting materials that are commerciallyavailable to form a thin film of semiconductor bearing materialoverlying a suitable substrate member. The thin film of semiconductorbearing material can be further processed to form a semiconductor thinfilm material of desired characteristics, such as atomic stoichiometry,impurity concentration, carrier concentration, doping, and others. In aspecific embodiment, the present invention provides a resultingstructure that is reliable and free from berm structures and the like.In preferred embodiments, the present invention uses commonly used toolsand process technology. Depending on the embodiment, one or more of thebenefits can be achieved. These and other benefits will be described inmore detailed throughout the present specification and particularlybelow.

Merely by way of example, the present method and materials includeabsorber materials made of copper indium disulfide species, copper tinsulfide, iron disulfide, or others for single junction cells or multijunction cells.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified flowchart illustrating a method of fabricating athin film photovoltaic cell according to an embodiment of the presentinvention;

FIGS. 2-4, 4A, 5, 5A, 6, 6A, and 7-11 are schematic diagramsillustrating a method comprising a series of processes and structuresfor fabricating a thin film photovoltaic cell according to certainembodiments of the present invention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

The present invention relates generally to photovoltaic materials andmanufacturing method. More particularly, the present invention providesa method and structure for fabricating thin film solar cells. Merely byway of example, the present method includes patterning electrodematerial formed on a soda lime glass substrate using electromagneticradiations and processing the electrode material free from bermstructures for manufacture of thin film photovoltaic cells, but it wouldbe recognized that the invention may have other configurations.

FIG. 1 is a simplified flowchart illustrating a method of fabricating athin film photovoltaic cell according to an embodiment of the presentinvention. This diagram is merely an example, which should not undulylimit the scope of the claims herein. The method 1000 includes thefollowing processes:

1. Process 1010 for providing a soda lime glass substrate with a surfaceregion;

2. Process 1020 for forming a lower electrode layer overlying thesurface region;

3. Process 1030 for subjecting the lower electrode layer with a laserradiation to ablate one or more patterns;

4. Process 1040 for processing the lower electrode layer to remove oneor more berm structures of the one or more patterns;

5. Process 1050 for treating the lower electrode layer with the one ormore patterns free of the one or more berm structures;

6. Process 1060 for forming a layer of photovoltaic material comprisingan interconnect structure based on each of the one or more patterns;

7. Process 1070 for forming a first zinc oxide layer overlying the layerof photovoltaic material;

8. Process 1080 for performing other steps.

The above sequence of processes provides a method of patterning anelectrode layer and processing the electrode layer to form one or morepatterns free of berm structures for manufacture of thin filmphotovoltaic cells according to an embodiment of the present invention.In a specific embodiment, the method includes applying laser radiationsfor ablating the one or more patterns from a continuous electrode layer.In another specific embodiment, the method also includes usingmechanical brush device for processing the one or more patterns. Otheralternatives can also be provided where processes are added, one or moreprocesses are removed, or one or more processes are provided in adifferent sequence without departing from the scope of the claimsherein. For example, a barrier layer can be formed before the lowerelectrode layer is formed. More functional layers with differentmaterial compositions can be inserted between the layer of photovoltaicmaterial and the first zinc oxide layer, and so on. Further details ofthe method can be found throughout the present specification and moreparticularly below.

At Process 1010, a soda lime glass substrate is provided. This processcan be visually illustrated by FIG. 2. FIG. 2 is a simplified diagramillustrating a soda lime glass substrate provided for fabricating a thinfilm photovoltaic cell according to an embodiment of the presentinvention. This diagram is merely an example, which should not undulylimit the scope of the claims herein. One of ordinary skill in the artwould recognize many variations, alternatives, and modifications. Asshown, the soda lime glass substrate 100 including a surface region 101is provided. The soda lime glass has been widely used as window glass.One important reason for choosing the soda lime glass as substrate forforming thin film photovoltaic cells other than simple economicalconcern is a positive influence of alkaline ions (e.g., Na⁺) on thegrain growth of high efficiency thin film photovoltaic materials. Forexample, polycrystalline compound semiconductor films of chalcopyritestructure CuIn(Ga)Se₂ or CuInSe₂ materials can be formed on soda limeglass substrates with coarse grain sizes of 1 microns or larger so thathigh cell current can be collected with these photovoltaic films to havelight-conversion efficiencies of 17% or above. Without the doping ofsodium atoms, the same film material formed on other type of substratehas much finer sized grains. In certain implementations, the surfaceregion 101 is subjected to certain pre-treatment process so that thesurface region 101 is cleaned substantially free from surfacecontaminations, greases, dirts, dusts and particles having sizes largerthan 3 microns.

At Process 1020, a lower electrode layer is formed overlying the surfaceregion of the soda lime glass substrate. This process can be visuallyillustrated by FIG. 3. As shown, the lower electrode layer 200 is formedoverlying the surface region 101 of the soda lime glass substrate 100.The lower electrode layer 200 is to serve a back electrode for thin filmphotovoltaic cells to be formed in subsequent processes. Here “lower” ismerely a word for current example of forming a thin film on substrate,the thin film is to become a bottom solar cell. “Lower” electrode maycorrespond to an “upper” or “front” electrode that is located on top ofa window layer. While when the substrate is used as “superstrate” in anapplication of forming a top solar cell, the lower or upper electrodescan be disposed in opposite way. In certain cases when no confusion,only electrode layer is mentioned. In particular, either the lower orupper electrode layer can be optically transparent. For example, thelower electrode layer is made of molybdenum material with thicknessranging from 0.2 to 1 microns. In other examples, transparent conductiveoxide can be used as the material for upper electrode layer. In certainimplementations, the formation of the electrode layer can be achievedusing a deposition process, such as sputtering, plating, evaporation,plasma deposition, and the like and any other suitable technique. Ofcourse, there can be other variations, modifications, and alternatives.

In the next process (1030), the method 1000 includes subjecting thelower electrode layer with a laser radiation to ablate one or morepatterns. This laser patterning or ablation process can be visuallyillustrated by FIG. 4. FIG. 4 is a schematic diagram illustrating aprocess for fabricating a thin film photovoltaic cell according to anembodiment of the present invention. This diagram is merely an example,which should not unduly limit the scope of the claims herein. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. As shown, the lower electrode layer 200 is subjectedto a laser radiation 120 at certain predetermined locations. The laserradiation 120 can be a beam of pulsed laser or CW laser. The laser beamcan be aligned from above the lower electrode layer 200 or from a backsurface region of the soda lime glass substrate 100 for the glass isoptically transparent. This laser alignment option is depended on thedesign of a manufacture system and specific thin film growth processes.Typically the laser beam is generated from a Nd: YAG infrared Q-Switchedpulse laser source with wavelength of about 1065 nm. Of course, othertypes of laser sources with different wavelength or pulse rate can alsobe used depending on applications.

In one embodiment, the laser beam 120 irradiating the lower electrodelayer 200 causes an ablation process in which a portion of the lowerelectrode layer under the laser beam is removed from the soda lime glasssubstrate 100. In particular, the laser energy causes vaporization ofelectrode layer material, e.g., molybdenum, under a beam spot or simplyblows away from the substrate 100. The laser beam 120 can be scannedalong a predetermined pattern and subsequently additional amount ofelectrode layer material is removed. Each time after the laser beamablates a spot of electrode layer material, the beam is moved (may bepulsed OFF) to a next spot, then the laser power is pulsed ON toirradiate the new spot again to cause the electrode layer material underthe new spot to be removed. As a result, the electrode layer 200, whichis initially deposited as a continues film overlying the surface region101 of the soda lime glass substrate 100, is going through a laserpatterning process to form one or more patterns (or laser ablatedpatterns).

As shown in the side view portion of the FIG. 4, one of the one or morepatterns 250 is schematically illustrated, separating the electrodelayer 200 into a left portion 200A and a right portion 200B. An enlargedtop view shows more details of a circled portion of a particular pattern250 that separates the lower electrode layer 200 to the two portions200A and 200B. In particular, the enlarged view shows that the pattern250 is actually a continuous line with a width of about 25 to 50 micronsof the lower electrode layer with being substantially removed from theglass substrate by the laser ablation process. As a result, a streetstructure is formed within the electrode layer 200. In certainembodiments, multiple streets with an average separation of about 6 mmare formed in the electrode layer overlying the whole surface region ofthe soda lime glass substrate, defining a stripe-shaped cell betweeneach neighboring streets.

Due to laser beam spatial profile and pulse/scan variation, one or moreberm structures 255 are formed within the pattern 250. In a specificembodiment, the one or more berm structures 255 usually are located nearedges of the pattern 250, while some may also be left near the middleregion of the pattern 250. As shown, the one or more berm structures 255have irregular shapes. Depending on the applications, the one or moreberm structures 255 may include residue material of the electrode layer250 or contaminants from a system housing the soda lime glass substrate.Because of the berm structures 255 are electrically conductive, they maycauses electrical shorting of thin film devices if they are notsubstantially cleaned or freed by a suitable process.

FIG. 4A is a microscope image showing a laser ablated pattern formed ona thin film over a glass substrate. As shown, the laser ablated patternis created by irradiating a round laser spot on the thin film to removethe thin film material under the spot at least partially. Additionally,the laser spot is allowed to scan from one spot to next, therebyremoving thin film material along the way. Provided a certain scanningspeed of the laser beam, a street or a channeled pattern is formed. As atop view in FIG. 4A, the street 255 corresponds to the laser ablatedpattern 250 in the lower electrode layer 200 seen as a side view in FIG.4. However, imperfection during the laser ablation process may leavecertain amount of residue/redeposit or un-removed portion of the thinfilm material forming one or more berm structures 255 inside or aroundthe laser ablation pattern 250. These berm structures 255 may cause thinfilm device degradation, shorting or other problems. Embodiments of thepresent invention provide a method to substantially clean the laserablation pattern free from these berm structures. More detaildescriptions on the method can be found throughout this specificationand more specifically below.

In the next process 1040, the method 1000 includes processing the lowerelectrode layer having one or more patterns to remove the one or moreberm structures therein. This process can be visually illustrated byFIG. 5. FIG. 5 is a schematic diagram illustrating a process forfabricating a thin film photovoltaic cell according to an embodiment ofthe present invention. This diagram is merely an example, which shouldnot unduly limit the scope of the claims herein. One of ordinary skillin the art would recognize many variations, alternatives, andmodifications. As shown in FIG. 5 a specific embodiment of the method1000 provides a mechanical brush device 300 disposed above the lowerelectrode layer 200. The mechanical brush device 300 includes a rotor301 carrying an outer edge comprising a plurality of bristles 305. Inone embodiment, the rotor 301 is powered to rotate along clockwisedirection 310 and at the same time is configured to laterally move alonga direction 320 which is substantially in parallel to the surface of thesoda lime glass substrate. In a specific embodiment, the brush movingdirection 320 can be either parallel or perpendicular to the laserablation pattern 250 for the purpose of effectively removing the debrisor particles inside the pattern. Also shown, a sprayer 350 is associatedwith the operation of the mechanical brush device 300 to provide aliquid, de-ionized water in a preferred embodiment, during the brushingprocess.

In certain implementation of the process 1040, the mechanical brushdevice 300 can be disposed to a proper height above the lower electrodelayer 200 and rolling the plurality of bristles 305 with a predeterminedrotation speed (along a direction 310) while at the same time movinglaterally with a predetermined lateral speed (along a direction 320).Subsequently, the mechanical brush device 300 is configured to adjustits height and lateral moving direction so that the one or more bermstructures 255 within or around the one or more patterns 250 in variousorientations and densities can be removed properly and as completely aspossible. Of course, there can be other variations, alternatives andmodifications in the control of rotation/lateral direction/speed, andconfigurations of the mechanical brush device including relativeposition of the rotor, a length of each bristle, supply of liquid fromthe sprayer 350, and so on. For example, the length of the brushbristles can be chosen to be sufficient to reach the depth of the laserscribed trench so that it can substantially clean up the debris (causedby laser ablation) inside the scribed region in addition to removing theberm structures on the surface region.

In a specific embodiment, the plurality of bristles 305 are made of anylon material. The mechanical strength of the nylon-based bristlesprovides necessary forces to remove the one or more berm structureswhich are scattered around and bonded to the substrate with relativesmall forces. While the nylon-based bristles also have relativeflexibility by their nature, depending further on how to group a certainnumber of bristles together and how distribute them around the outeredge of the mechanical brush device 300, so that the forces generated bythese bristles would not cause injures to the remaining portions oflower electrode layer (e.g., 200A and 200B), which bonded to areattached to the substrate with much stronger forces. The mechanicalbrush device 300 including nylon-based bristles 305 according to anembodiment of the invention is able to consistently remove the one ormore berm structures 255 from the one or more patterns 250 of the lowerelectrode layer made of molybdenum material.

In an alternative embodiment, the mechanical brush device can be appliedfrom both sides of the transparent substrate. As schematically shown inFIG. 5A, which is a side view illustrating a substrate being transferredalong a plurality of rollers within a batch system. In this figure, onemechanical brush device 300A including a water sprayer 350A is appliedfrom a top surface region 201 and another mechanical brush device 300B,both of which can be substantially the same as the mechanical brushdevice 300, is applied from bottom surface region of the substrate. Inone example, the top surface region 201 is a surface of the lowerelectrode layer 200 overlying the substrate 100. In another example, thetop surface region 201 includes one or more portions being part of theone or more patterns 250 formed within the lower electrode layer 200.

Referring to FIG. 1, the method 1000 further includes a process 1050 oftreating the lower electrode layer with the one or more patterns free ofthe one or more berm structures. This process can be visuallyillustrated by FIG. 6, which is a schematic diagram showing a processfor fabricating a thin film photovoltaic cell according to an embodimentof the present invention. This diagram is merely an example, whichshould not unduly limit the scope of the claims herein. One of ordinaryskill in the art would recognize many variations, alternatives, andmodifications. As shown in a specific embodiment, part of the treatmentprocess 1050 involves a clean process during which the soda lime glasssubstrate 100 coated with an electrode layer 200 is exposed to acleaning liquid 400. In one implementation, the cleaning liquid 400comprises at least DI-water that physically wash out and reactivelydesorb surface residues. Subsequently, another part of the treatmentprocess 1050 involves a process of applying an air knife blower toremove moisture and any dusts left on a surface region of the electrodelayer 200.

In one implementation, as schematically shown in FIG. 6, a gas knifeblower 360 is disposed near the surface region of the electrode layer200 including one or more patterns 250 after the cleaning process usingthe cleaning solution 400. In one example, the gas knife 360 is an airknife with an elongated nozzle capable of providing a faceted profile ofhigh speed air flow 365. The impact air flow 365 with the facetedprofile is very effective for drying and cleaning the surface regionincluding one or more (stripe shaped) patterns. In another example, drynitrogen can be the gas in the gas knife. In one embodiment, the airknife blower 360 is capable of adjusting an angle relative to thesurface region 201 for achieving a desirable drying/cleaning effect. Forexample, the angle between the faceted profile of the air relative tothe surface can be adjusted from 90 degrees to somewhat 45 degrees or 30degrees and lower to enhance the drying effect. In another example, anangle between the air flow direction and the laser scribing pattern canalso be adjusted between 0 to 90 degrees to enhance the debris cleaningeffect. In an alternative embodiment, air pressure control of the airknife blower 360 can be used during the debris removal process,especially for removing debris inside the laser scribed pattern region.In a specific embodiment, using the air knife blower 360 for drying thesurface region can substantially remove any liquid including theresidues of the cleaning liquid 400, water droplets, or other chemicalsin liquid forms. In another specific embodiment, using the air knifeblower 360 to remove the liquid introduced in the treating process canbe accomplished by direct blowing away physically and substantially freefrom causing any evaporation. Thus, the drying effect according to theabove implementation of embodiments of the invention results insubstantially free of any moisture residue on the lower electrode layerincluding one or more patterns.

In another implementation, as schematically shown in FIG. 6A, both sidesof the substrate can be applied with the air knife blowers in the abovedrying/cleaning process. As shown, a substrate being transferred along aplurality of rollers within a batch system. The substrate has a topsurface region 201 which is essentially a surface of the lower electrodelayer 200 overlying the soda lime glass substrate 100 in FIG. 5. One airknife blower 360A is applied from above the top surface region 201 andanother air knife blower 360B is applied from the bottom of thesubstrate. Essentially, the treating process 1050 is a combined processincluding exposing the substrate to a cleaning liquid 400 and using anair knife blower 360 to dry the substrate including the lower electrodelayer 200 with one or more patterns 250. The treatment process resultsin the lower electrode layer 200 with one or more patterns 250substantially free from any one or more berm structures 255 and anymoisture residues.

Referring to FIG. 1 again, the method 1000 includes a process (1060) offorming a layer of photovoltaic material overlying the electrode layer.This process can be visually illustrated by FIG. 7, which is a schematicdiagram showing a process for fabricating a thin film photovoltaic cellaccording to an embodiment of the present invention. This diagram ismerely an example, which should not unduly limit the scope of the claimsherein. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. As shown, a layer ofphotovoltaic material 500 is formed overlying the lower electrode layer200. In particular, before or during the process 1060 of the formationof the layer of photovoltaic material 500, a pattern 250 formed by laserablation (process 1030) in the lower electrode layer 200 can be filledwith a conductive material to form an interconnect structure 270. Theinterconnect structure can serve as an electrical lead for collectingcurrent from a thin film solar cell to be formed with the layer ofphotovoltaic material. In a specific embodiment, the layer ofphotovoltaic material 500 is made of copper indium diselenide (CIS)material using a sputtering and a thermal annealing based selenizationprocess. In another specific embodiment, the layer of photovoltaicmaterial 500 comprises a copper indium gallium diselenide (CIGS)material, or copper indium disulfide material using one or more suitablethin film deposition processes. In one typical implementation, the layerof photovoltaic material 500 is a p-type semiconductor material actingas an light absorber of a thin film photovoltaic device. In oneembodiment, with a certain amount of sodium content doped therein, thelayer of CIGS material formed on (the lower electrode layer over) thesoda lime glass substrate can have large grain sizes larger than 1microns. Therefore, high cell current can be expected for achieving 17%or greater efficiency for the resulted thin film solar cell.

Although the above has been generally described in terms of a specificstructure for CIS and/or CIGS thin film cells, other specific CIS and/orCIGS configurations can also be used, such as those noted in U.S. Pat.No. 4,612,411 and U.S. Pat. No. 4,611,091, which are hereby incorporatedby reference herein, without departing from the invention described bythe claims herein.

Furthermore, the method 1000 includes a process (1070) of forming anupper electrode layer over the layer of photovoltaic material. Here theupper electrode layer or the second electrode layer is a first zincoxide layer which is a kind of transparent conductive oxide or TCO. Asshown in FIG. 8, subsequent to process 1060, the process 1070 leads to aformation of the second electrode layer 600 overlying the layer ofphotovoltaic material 500. FIG. 8 is merely an example, which should notunduly limit the scope of the claims herein. One of ordinary skill inthe art would recognize many variations, alternatives, andmodifications. In a specific embodiment, the second electrode layer 600is a first zinc oxide layer. In one example, the first zinc oxide layeris formed using a metal-organic chemical vapor deposition (MOCVD)technique within a batch system. The formed first zinc oxide layer byMOCVD is a rough layer, which can diffuse the incoming light byscattering, increasing the efficiency of solar cells. Additionally, thefirst zinc oxide layer 600 can be mechanically patterned to form one ormore patterns which in additions are used to form at least anotherinterconnect structure 670 for the thin film photovoltaic cell, shown asan example in FIG. 8.

The method 1000 then can include a process 1070 for any additional stepof fabricating a thin film photovoltaic device. For example, the process1070 can be another mechanical patterning for configuring the second orupper electrode layer, can be a mechanical isocut process for preparingone or more unit cells, and can be a mechanical bus pad cleaning processfor assembling the one or more unit cells. Of course, there can be manyvariations, alternatives, and modifications.

In an alternative embodiment, the method 1000 may include a process offorming a barrier layer directly onto the surface region (after apre-washing treatment process) of the soda lime glass substrate beforethe process 1020 for forming a lower electrode layer. FIG. 9 shows aprocess of fabricating a thin film photovoltaic cell on soda lime glasssubstrate according to an alternative embodiment of the presentinvention. This diagram is merely an example, which should not undulylimit the scope of the claims herein. One of ordinary skill in the artwould recognize many variations, alternatives, and modifications. Asshown, a barrier layer 150 is inserted between the lower electrode layer200 and the surface region 101 of the soda lime glass substrate 100.Because excessive, uncontrolled amount of sodium may reduce the grainsizes of the photovoltaic thin film grown on the soda lime glasssubstrate, the barrier layer 150 is applied for preventing sodiumelement from diffusing into the upper layers especially the layer ofphotovoltaic material. In one embodiment, the barrier layer 150 is alayer of silicon dioxide formed by a sputtering process, which serves asan effective sodium diffusion barrier with a thickness of only about 200Angstroms or greater. Other materials including aluminum oxide, siliconnitride, titanium nitride, titanium oxide, or zirconium oxide also canbe used depending on applications. In an alternative embodiment, thebarrier layer property can be engineered or adjusted to improve theeffectiveness of blocking sodium ion diffusion from glass intophotovoltaic active layers. For example, the barrier layer density canbe a factor utilized. Higher barrier layer density can be used to raisethe diffusion barrier and limit the amount of sodium diffusion.

In another alternative embodiment, the method 1000 can include a processof forming a cadmium sulfide layer overlying the layer of photovoltaicmaterial before forming the first zinc oxide layer. In particular, asshown in FIG. 10 the layer of photovoltaic material 500 is a layer ofcopper indium diselenide material overlying the lower electrodemolybdenum layer 200. The cadmium sulfide layer 505, characterized as awide bandgap semiconductor, is formed over the layer of copper indiumdiselenide material 500 to serve as a window layer for the thin filmphotovoltaic cell while the layer of copper indium diselenide material500 acting as an absorber layer. In certain embodiments, the cadmiumsulfide layer 505 is considered as one part of the layer of photovoltaicmaterial which is formed using a multilayer deposition and treatmentprocess. In one example, the cadmium sulfide layer 505 can be formedusing sputtering, vacuum evaporation, or chemical bath deposition (CBD)techniques and doped with n⁺-type impurities for conductivity. Dependingon embodiments, the window layer can be selected from a group materialsconsisting of a cadmium sulfide (CdS), a zinc sulfide (ZnS), zincselenium (ZnSe), zinc oxide (ZnO), zinc magnesium oxide (ZnMgO), orothers.

In yet another alternative embodiment, the method 1000 can include aprocess of forming a second zinc oxide layer before forming the firstzinc oxide layer. As shown in FIG. 11 the second zinc oxide layer 605 isfirst formed over the layer of photovoltaic material, or in particularover the cadmium sulfide layer 505, and the first zinc oxide layer 600is formed over the second oxide layer 605. The layer of photovoltaicmaterial 500 is a layer of copper indium diselenide material overlyingthe lower electrode molybdenum layer 200. In a specific embodiment, thesecond zinc oxide layer 605 has a higher resistivity than the first zincoxide layer 600. Functionally, the second zinc oxide layer 605 playsmore a role of barrier/protection layer while the first zinc oxide layer600 with lower resistivity plays more a role of conductive electrodelayer. In certain embodiment, the second zinc oxide layer 605 is alsoformed using a metal-organic chemical vapor deposition (MOCVD) techniquewithin a batch system.

Although the above has been illustrated according to specificembodiments, there can be other modifications, alternatives, andvariations. It is understood that the examples and embodiments describedherein are for illustrative purposes only and that various modificationsor changes in light thereof will be suggested to persons skilled in theart and are to be included within the spirit and purview of thisapplication and scope of the appended claims.

1. A photovoltaic device comprising: a substrate having a surfaceregion; a first electrode layer having a first thickness disposed overthe surface region and comprising: one or more patterns; an interconnectstructure formed by filling a pattern, wherein a height of theinterconnect structure is substantially equal to the first thickness; aphotovoltaic layer disposed over the lower electrode layer and theinterconnect structure; and a second electrode layer having a secondthickness disposed over the photovoltaic layer.
 2. The photovoltaicdevice of claim 1 further comprising a second interconnect structuredisposed within the second electrode layer, wherein a height of thesecond interconnect structure is substantially equal to the secondthickness.
 3. The photovoltaic device of claim 1 further comprising abarrier layer disposed between the surface region of the substrate andthe first electrode layer.
 4. The photovoltaic device of claim 1 furthercomprising a window layer disposed between the photovoltaic layer andthe second electrode layer.
 5. The photovoltaic device of claim 1wherein the substrate comprises soda lime glass material.
 6. Thephotovoltaic device of claim 1 wherein the first electrode layercomprises molybdenum.
 7. The photovoltaic device of claim 1 wherein thephotovoltaic layer comprises copper indium gallium diselenide (CIGS)material.
 8. The photovoltaic device of claim 1 wherein the secondelectrode comprises a transparent conductive oxide material.
 9. A methodcomprising: providing a substrate having an upper surface and anopposing lower surface; forming a first electrode layer overlying theupper surface, the first electrode layer having a first thickness;forming one or more patterns in the first electrode layer; filling atleast one pattern, from the one or more patterns, with a conductivematerial to form a first interconnect structure having a first height,wherein the first height is substantially equal to the first thickness;forming a photovoltaic layer over the first electrode; and forming asecond electrode layer having a second thickness over the photovoltaiclayer.
 10. The method of claim 9 wherein the substrate comprises sodalime glass material.
 11. The method of claim 9 wherein forming one ormore patterns further comprises: subjecting the first electrode layer toone or more pulses of electromagnetic radiation from a laser source; andremoving one or more portions of the first electrode layer to form theone or more patterns.
 12. The method of claim 9 further comprising priorto forming the interconnect structure, processing the first electrodelayer comprising the one or more patterns using a mechanical brushdevice to remove the one or more berm structures.
 13. The method ofclaim 9 further comprising forming a second interconnect structuredisposed in the second electrode layer.
 14. The method of claim 9further comprising forming a barrier layer overlying the upper surfaceof the substrate prior to forming the first electrode layer.
 15. Themethod of claim 9 further comprising forming a window layer overlyingthe photovoltaic layer prior to forming the second electrode layer. 16.The method of claim 9 further comprising: cleaning the upper surface ofthe substrate and the first electrode layer using a cleaning liquid; andremoving residual cleaning liquid including liquid droplets from theupper surface of the substrate and the first electrode layer using a gasknife configured to provide a facet profile of dry air with adjustableangles relative to the upper surface of the substrate.
 17. The method ofclaim 9 further comprising forming a transparent oxide layer overlyingthe photovoltaic layer prior to forming the window layer.
 18. The methodof claim 9 wherein the first electrode layer comprises molybdenum. 19.The method of claim 9 wherein the second electrode layer comprises atransparent conductive oxide material.
 20. The method of claim 9 whereinthe photovoltaic layer comprises copper indium gallium diselenide (CIGS)material.